View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Nottingham ePrints Whiley, Henry (2013) Flavour development of East Midlands cheeses and evaluation of flavour producing microorganisms in a small scale real-cheese model. MRes thesis, University of Nottingham. Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/13234/1/Everything.pdf Copyright and reuse: The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. · Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. · To the extent reasonable and practicable the material made available in Nottingham ePrints has been checked for eligibility before being made available. · Copies of full items can be used for personal research or study, educational, or not- for-profit purposes without prior permission or charge provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. · Quotations or similar reproductions must be sufficiently acknowledged. Please see our full end user licence at: http://eprints.nottingham.ac.uk/end_user_agreement.pdf A note on versions: The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher’s version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. For more information, please contact [email protected] FLAVOUR DEVELOPMENT OF EAST MIDLANDS CHEESES AND EVALUATION OF FLAVOUR PRODUCING MICROORGANISMS IN A SMALL SCALE REAL-CHEESE MODEL HENRY WHILEY, B.Sc. (Hons) Thesis submitted to the University of Nottingham for the degree of Master of Research July 2013 Supervisor Prof. Christine E. R. Dodd Division of Food Sciences School of Biosciences The University of Nottingham ABSTRACT Stilton is a blue-veined cheese made from pasteurised milk. The diversity of the microflora found within the cheese helps develop the unique flavour and aroma of Stilton compared to other blue cheese. However, this flora is not controlled and so product may be variable. A small-scale cheese model was developed to allow examination of the effect of different microflora on flavour production in a controlled way. Texture analysis, water activity and viable count of the cheese models were compared to commercial cheeses in order to optimise the model. The final model had the hardness of Danish Blue and the water activity of Stilton. The growth of lactic acid bacteria through the cheese making process was monitored and showed a characteristic reduction after salting. Changes in total aerobic count and yeast and moulds after salt addition and handling showed the ease with which the cheese can become contaminated with external flora such as yeasts and moulds even under aseptically manipulated conditions. Solid Phase Microextraction Gas Chromatography Mass-Spectrometry was used to evaluate the flavour volatiles produced when milk and cheese were inoculated with different microorganisms. Some yeast species such as Trichosporon beigleii inhibited the metabolism of P. roqueforti within the models, where as others such as Debaryomyces hansenii aided the metabolism of compounds in the models to develop different flavour volatiles. Overall a small-scale blue cheese model was produced and can be used to understand the role of different organisms in the development of the flavour and aroma of blue cheeses in the future. ACKNOWLEDGEMENTS I would like to thank my supervisors Prof. Chris E. R. Dodd and Dr Kostas Gkatzionis for their help and support with both the practical side and the write-up of my thesis. I would also like to thank Rob Linforth for all his help with statistics and the flavour volatile analysis part of my project. I am grateful to Joe Schneider for his contribution of the Stichelton protocol. My thanks goes to David Fowler, Nicola Cummings, Wendy Fielder and Lorraine Gillet for their support in and around the Food Microbiology laboratory, and to all the students and staff members within the Food Science building for the help they have given me and for making my time during my MRes an enjoyable one. Special thanks go to Daniel Freeman for the assistance that he has given me in the lab during the year and Sarah Pingiori for the proof-reading of my thesis. TABLE OF CONTENTS ABSTRACT.............................................................................................. i ACKOWLEDGEMENTS....................................................................... ii TABLE OF CONTENTS........................................................................ iii LIST OF FIGURES................................................................................. vi LIST OF APPENDICES......................................................................... viii 1 INTRODUCTION................................................................................ 1 1.1 STILTON................................................................................. 1 1.1.1 Description of Stilton................................................ 1 1.1.2 History of Stilton....................................................... 1 1.1.3 Stilton Production..................................................... 2 1.1.4 Microflora of Stilton................................................. 3 1.1.4.1 Bacterial Flora of Stilton........................... 3 1.1.4.2 Fungal Flora of Stilton.............................. 5 1.2 FLAVOUR ANALYSIS........................................................ 6 1.2.1 Stilton Aroma........................................................... 6 1.2.2 Solid Phase Microextraction Gas Chromatography- Mass Spectrometry (SPME GC-MS).................... 7 2 MATERIALS AND METHODS........................................................ 9 2.1 MEDIA AND CHEMICALS................................................. 9 2.2 STRAINS AND CULTURE................................................... 9 2.3MILK MODEL FOR VOLATILE PRODUCTION............... 10 2.3.1 Preparation of the Lactococcus Inoculant................ 10 2.3.2 Preparation of the Penicillium Inoculant.................. 10 2.3.3 Preparation of the Yeast Inoculant........................... 11 2.3.4 Inoculation and Incubation of the Milk Model....... 11 2.4 CHEESE PRODUCTION MATERIALS............................. 11 2.5 CHEESE SAMPLES............................................................. 12 2.6 SOLID PHASE MICROEXTRACTION GAS CHROMATOGRAPHY-MASS SPECTROMETRY.... 13 2.7 VIABLE COUNT................................................................. 14 2.8 pH TESTING........................................................................ 15 2.9 TEXTURE ANALYSIS....................................................... 15 2.10 WATER ACTIVITY.......................................................... 16 3 RESULTS........................................................................................... 17 3.1 CHEESE PRODUCTION METHOD.................................. 17 3.1.1 Initial Cheese Protocol........................................... 17 3.1.2 Impact of Starter Culture....................................... 19 3.1.3 Altering the Stichelton Protocol For a Small-Scale Model................................................................. 21 3.1.4 Removal of P. Roqueforti...................................... 22 3.1.5 Effect of Pressing the Cheese................................ 28 3.1.6 Effect of Maturation.............................................. 31 3.1.9 Final Small-Scale Cheese Model.......................... 38 3.2 SOLID PHASE MICROEXTRACTION GAS CHROMATOGRAPHY-MASS SPECTROMETRY... 39 3.2.1 Milk Samples.......................................................... 39 3.2.2 Cheese Samples...................................................... 42 3.2.3 Comparison of Milk and Cheese Samples............. 46 4 DISCUSSION..................................................................................... 50 5 BIBLIOGRAPHY............................................................................. 56 APPENDICES..................................................................................... 61 LIST OF FIGURES Figure 1: The blue cheese production protocol........................................ 18 Figure 2: The average change in pH of two replicates............................. 20 Figure 3: Two cheeses having been engulfed by P. roqueforti................ 23 Figure 4: A white cheese with P. roqueforti contamination.................... 24 Figure 5: The texture of commercial cheese compared to the 1st small- scale cheese................................................................................... 25 Figure 6: The water activity of commercial cheese compared to the 1st small scale cheese......................................................................... 27 Figure 7: The texture of the pressed cheese compared to the un-pressed cheese............................................................................................ 29 Figure 8: The water activity of commercial cheese compared to the pressed cheese............................................................................... 30 Figure 9: The texture of the pressed cheese compared to the commercial cheese.......................................................................